In the human metabolism of proteins, the principle waste products are urea and creatinine. The normal daily production of urea is 30 grams and 1.5 grams of creatinine. In the healthy human, these materials are removed from the blood stream by the kidneys and excreted from the body in the urine. In the case of a diseased or damaged kidney that is unable to perform its normal function, current medical practice provides for the removal of urea and creatinine by means of the extracorporeal treatment of the patient's blood in a renal dialysis device employing specially designed semipermeable membranes. The blood circulates in contact with one face of a membrane, the other face of which is in contact with an aqueous solution of chemical composition similar to that of blood. In this aqueous "dialysis bath" the concentration of urea and creatinine must be kept as low as possible in order for the urea and creatinine in the blood to continue to flow across the membrane as a result of a high concentration gradient. This requires either the replacing of the dialysis bath by a new bath when the gradient decreases, or the treatment of the dialysis bath in order to either completely or partially remove the urea and creatinine. One method used for lowering the waste product concentration in the used bath consists of introducing it into a storage reservoir of fresh solution before it is reused, but this soon leads to the use of large volumes of dialysis liquid which must in any case ultimately be discarded. A number of attempts have been made to remove urea and creatinine by treating the used dialysis bath with ion exchange resins or activated charcoal, and a method has been cited (U.S. Pat. No. 4,012,317, Mar. 15, 1977, Kuntz et al) that uses a polymer for removing urea. However, the efficiency of all previously tried compounds, especially in the case of urea, has proved to be quite low.
The present invention pertains to a method for removing urea and creatinine from aqueous solutions by contacting such solutions with a polymer selected from the group consisting of:
1. p-Mercapto polystyrene PA1 2. p-Mercaptoacetic polystyrene PA1 3. Dinitro-p-mercaptoacetic polystyrene PA1 4. p-Nitropolystyrene PA1 5. p-Amino polystyrene